Adjustable linear cam drive



Oct. 25, 1960 a. M. STOCKWELL 2,957,357

ADJUSTABLE LINEAR CAM DRIVE Filed Aug. 13, 1958 FIE E INVENTOR. 61.40: MSrocwwru.

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ADJUSTABLE LINEAR CAM DRIVE Glade M. Stockwell, Cedar Rapids, Iowa,assignor to Collins Radio Company, Cedar Rapids, Iowa, a corporation ofIowa Filed Aug. 13, 1958, Ser. No. 754,874

2 Claims. (CI. 74-55) matching electrical components with mechanicallinear cam drives so that a desired mechanical rotation of the cam gavea required electrical performance. There are various methods that havebeen known prior to this invention which the manufacturer can follow tomatch the rise of the cam with the electrical component, namely: (1) thecam can be modified to match the electrical performance of thecomponent, (2) the dial or other controlling means can be calibratedindividually for each electrical component, (3) an arbitrary scale canbe correlated with the actual electrical performance by tabulated means,(4) the angular displacement of the cam may be modified to meet therequirements of the electrical component, or (5) the electricalcomponent can be adjusted to'conform with the mechanical drive. Thelatter method is generally used to match the two components; however,all of these methods are expensive and difficult to perform. It is anobject of this invention to provide a cam drive where the total movementof the follower can be adjusted and yet maintain linearity of themovement so that the indicator or dial or other controlling means neednot be changed or hand-calibrated to conform to the electricalcomponents.

' It is a further object of this invention to provide an adjustable camfollower which will permit an easy mechanical adjustment to provide forthe variations in electrical characteristics of the components withoutnecessitating recalibration of the mechanical scale or modification ofthe cam or cam drive.

Further objects, features, and advantages of this invention will becomeapparent from the following description and claims when read in view ofthe accompanying drawings, in which:

Figure 1 is a perspective view of one embodiment of the invention, and

Figure 2 illustrates a mathematical description of the operation of theinvention.

With reference to Figure 1, an adjustable linear cam drive is supportedby a frame or chassis 10. A slug-tuned coil 11 of a well-known type ismounted on chassis by a C type bracket 12. Bracket 12 includes C members13 surrounding the coil, and formed with a base 14 secured to thechassis by screws 15. A tubular core 16 of the coil permits theinsertion of a tuning slug 1'7 axially supported at one end by a shaft18.

A supporting member 19 threadedly receives the opposite end of shaft 18.Accordingly, movement of supporting member 19 moves the slug in or outof the tubular core, thus changing the inductance of the coil.

Supporting member 19 has a portion 20 slideably mouned in square slides21 and 22 attached to the chassis by means of screws 42. Dowel pins 23and 24 are States Patent Ofifice 2,957,357 Patented Get. 25, 1960mounted in the central portions of the respective slides 21 and 22 andextend through a pair of slots 25 and 26 in portion which supportsmember 19.

'A spring 43 between dowel pin 23 and the end of slot biases a camfollower surface 35 against a cam 33. The spring is retained againstdowel pin 23 by means of retaining pin 44 and is retained in the end ofslot 25 by a hole, not shown, longitudinally placed into the supportingmember. The slides and pins confine the movement of supporting member 19along the axis of the coil.

Another portion 27 of the supporting member 19 supports a cam followersector 28, a follower arm pivot 29, a follower arm locking assembly 30,31, 32 and a scale indicator 34. Follower sector 28 has a hole 45 at itscenter of curvature which receives a dowel pin 29 attached to thesupporting portion 27. A follower surface 35 of sector 28 is flat andsmooth. An arcuate scale part 33 of follower sector 28 containsgraduations which will be discussed in a subsequent section. Anindicator 34 is attached to supporting member 19 and cooperates with thescale.

A locking assembly 36 comprises a stud 32 attached to supporting portion27 and a washer and nut 31. They are tightened to prevent rotation ofsector 28 about its pivot 29.

A shaft 37 is rotatably mounted in a bearing 38 which is secured in thechassis. An involute cam 39 is fixed on the shaft and is in engagementwith and in the same plane as the follower arm. It is secured to theshaft by a set screw 42 transversely screwed through a collar 40 of thecam. A knob 41 is attached to an end of shaft 37.

In operation, the supporting member 19 is slideably moved along the axisof the coil by the action of the involute cam 39 against the flat linearportion of the follower sector 28. The total distance that the slug willmove for a given number of degrees rotation will depend on the angularsetting of the flat portion 35 of the follower sector. The setting canbe changed by loosening the nut 31 and physically rotating the sectorabout its pivot 29. The scale 33 in conjunction with indicator 41 can beused as a guide to determine the new or required setting. However,regardless of the angular setting of the follower sector, the movementof the supporting member 19 will always remain linear due to theinherent property of the involute cam acting against a fiat surface.

The operation of the involute cam and flat follower can be betterexplained by referring to Figure 2.

Mathematically, the involute of a circle is developed by unwrapping astring or similar substance from around the circumference of a circle.As it is being unwrapped, the end of the string will transcribe an arcof constantly and uniformly increasing radii. The arc thus formed is aninvolute curve of a circle. The curve thus developed is used as the camsurface of this invention.

If a cam is constructed with the involute as the engaging surface and isinitially rotated through an angle 0:, it will engage a flat-edgedfollower which is set at an angle Ad O, at point A. If the cam is thenfurther rotated through an angle 0, A will engage the follower, movingit back along the center point axis to A". The distance that thefollower is forced back is proportional to the increase in cam radiusA'O, which is also proportional to the tangent A'B'. Thus if thetangents AB, AB etc. increase linearly with equal degrees rotation, thecam radii will also increase linearly in like manner. It can also beseen that A'B increased in length over AB by the arcuate portion of thecircumference BB. This portion represents the portion of thecircumference that would be subtended by every angular rotation equal tothe angle 0. Therefore each tangent for every rotation 19 increases thesame amount.

The follower must be flat since it is confined to a direction of motionat angles to the contact point axis. Thus as the follower moves alongthe line Od the cam rotating in a counterclockwise direction, mustcontact the follower at higher and higher points as it moves throughsubsequent angles of 0. In the design of involute surfaces operating oninvolute gear teeth or straight-edge follower surfaces, a change ineffective pitch radius between an involute cam and its mating surfaceproduces a corresponding change in the distance the mating surface willtravel. If the pitch radius is increased the mating surface willincrease its travel by a corresponding amount. An increase or decreasein the angle of the follower of this invention will produce acorresponding increase or decrease in the pitch radius.

Since the radius of a straight follower is infinite, the line of centerswill be perpendicular to the movement of the follower and through thecenter of the base diameter circle of the involute cam. With a followerangle the line of centers (Figure 2) will intersect the tangent line ABat point P. The distance PO is defined as the pitch radius (R). If thefollower angle is changed to the tangent A'B' intersects the line ofcenters at P. Thus it can he obviously seen that the pitch radius hasbeen increased by increasing the angle of the contact point axis from 5to (p The above can be illustrated mathematically as follows:

If D is the base circle diameter of the involute cam then D =2R cos n5Db 7 COS 4n (1) Further if S is the total movement of the cam followerwith 360 rotation of the cam, and 0c is the number of degrees of actualrotation of the cam then Za-R 1 oz (2) cos j360 Substituting Equation 1in 2 S 1: 1rD oz 1 cos o 360 With any given values of D and a where S isthe new distance of movement of follower arm with cos From Equation 3the maximum movement of the follower arm can be calculated, or if thedistance is known, the follower angle 5 can be calculated. The cam andfollower are very adaptable where a scale has already been engraved orprinted, or a mechanical drive with a fixed angular displacement hasbeen designed, but it subsequently becomes necessary to move the tuningelement or slug a total distance slightly more or less than the originalsetting in order to allow the production electrical deviations in eachindividual tuning member to conform mechanically to the scale or drivemechanism. Since any change in the angular setting of the followersector will always maintain a linear movement there is no necessity ofeither constructing a new scale or drive on performing adjustments toother components in the circuit. This invention then allows a simplemechanical adjustment to displace the time-consuming practice ofredesigning or trimming coils or adjusting other elements in order thatthey will conform to the exerting scale or drive mechanism.

Although this invention has been described with respect to a particularembodiment thereof, it is not to be so limited as changes andmodifications may be made therein which are within the full intendedscope of the invention as defined by the appended claims.

I claim:

1. An adjustable linear cam drive comprising a mounting means, aninvolute cam rotatably mounted on said mounting means, a supportingmember slideably mounted on said mounting means, a flat cam followeradjustably mounted on said supporting means, said fiat portion engagingsaid involute surface of said involute cam, and a means for permittingadjustment of the flat cam to]- lower with respect to the direction ofmovement of said slideably mounted supporting means including a pivotpermitting rotatable adjustment of said follower sector and a lockingmeans for securing said adjustment.

2. An adjustable linear cam drive as claimed in claim 1 characterized inthat the fiat follower arm includes an indicating means for accuratelysetting the total travel of said supporting means.

References Cited in the file of this patent UNITED STATES PATENTS651,828 Copland June 19, 1900 1,810,985 Reichenbach June 23, 19312,119,567 Williams June 7, 1938 2,163,343 Leishman June 20, 19392,209,298 Martenis July 23, 1940 2,291,582 Plensler July 28, 19422,505,791 Rennick May 2, 1950 2,776,573 Willi Jan. 8, 1957 2,838,939Schlegal June 17, 1958

